When testing to determine the presence of a specific learning disability (SLD), it is important to remember certain key facts.
First, it is essential to have a clear definition of a SLD. The accepted definition stated in the Individuals with Disabilities Act (IDEA) is: “a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, which disorder may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or do mathematical calculations.” Such term “includes such conditions as perceptual disabilities, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia.” That is, there must be evidence of a cognitive processing deficit. It is important that the deficit be manifested functionally such that it clearly interferes with learning and performance. Moreover, the deficit in ability must be related theoretically with an academic subject that relies on this skill for success.
Second, there are times when the normative ability and achievement data do not match. For example, cognitive ability testing may indicate Average skills while achievement testing yields Above Average skills. Here, it is essential to keep in mind that overall ability scores like the IQ only explain 50% of the variations obtained. In the instance where achievement exceeds ability, other factors like good instruction, tutoring, practice, and the acquisition of compensatory strategies can result in better performance than would be expected given the Average ability testing. In addition, an unfortunate artifact of achievement test batteries is that the content of the items may underrepresent the difficulty level of the core curriculum, resulting in higher achievement scores that are discrepant from the classroom functional data. This situation, which has become more and more common, has been informally referred to as a curriculum-based learning disability. That is, the difficulty level of the curriculum overpowers some students’ ability to perform adequately even when that ability is Average. While lower achievement scores traditionally evoke thoughts of a learning disorder, they may also signal deficient executive function skills that interfere with accessing an individual’s full abilities. For example, the deficits in encoding and retrieving information efficiently in the short or long term may signal EF problems that look like a SLD.
The Pattern of Strengths and Weaknesses (PSW) approach to identifying a SLD is the most comprehensive method in that it includes normative data in the areas of ability and achievement, executive functions, and functional data. Unlike other methods, PSW does not rely solely on a formula and, instead, leans heavily on the experience, acumen, and clinical judgment of the professional evaluator to integrate all of the available information to make the best diagnosis possible.